Integrated storage devices, commonly referred to as integrated memory circuits, have long been in use for a wide number of applications in electronics, and their information storage capacity is in constant increase.
This is one reason why the manufacturers of integrated circuits have recently reported on the occasion of technical meetings, and less frequently actually produced, devices which are designed for storing more than one element of binary information in each of their storage elements. See, for example, the article "A Multilevel-Cell 32 Mb Flash Memory," ISSCC95, Session 7, February 1995, Paper TA 7.7. Such devices are commonly referred to as multi-level memories.
Increased storage capacity brings about, inter alia, an increase in the number of terminals (pins) on the assembled component, particularly in the number of address-dedicated pins. Even a moderately expanded storage capacity, say a doubled capacity, which would merely involve the addition of one address pin, may instead result in a far larger package having to be used. For example, a standard 32-pin package may turn out to eventually include 40 pins.
In other fields of microelectronics, solutions have been adopted which provide multiplexed terminals, that is, if there are eight data-dedicated terminals in a processor, and the internal word length is of thirty two bits, a word may be supplied to the processor in four time-successive steps through these eight terminals. In addition, there are integrated memory circuits of the serial type, i.e. wherein all the binary information relating to a terminal function--usually data and/or addresses--goes through the terminal itself in timed succession. This is the case, for instance, with an integrated circuit ST24E16 from SGS-THOMSON MICROELECTRONICS. Such solutions allow the number of terminals to be considerably reduced, but are too elaborate for the aforementioned problem, are fairly complicated and, therefore, occupy a larger semiconductor die area